Vacuum pump with two co-operating rotors

ABSTRACT

The invention relates to a vacuum pump ( 1 ) comprising a pump chamber casing ( 5 ) accommodating two co-operating rotors ( 2, 3 ) which are respectively arranged on a shaft ( 8, 9 ); a bearing/gear chamber ( 6 ) adjacent to the pump chamber casing ( 5 ) in which the rotor shafts ( 8, 9 ) are cantilevered and provided with a synchronisation gear ( 17 ); a drive motor ( 25 ) whose drive shaft ( 28 ) extends parallel to the rotor shafts ( 8, 9 ) and is provided with a drive gear ( 35 ); also comprising a gear stage ( 37 ) between the drive shaft ( 28 ) and one of the rotor shafts ( 8, 9 ). In order to provide a machine of this type which can be embodied in a compact form, the drive gear ( 35 ) of the drive shaft ( 28 ) engages directly with a driven gear ( 36 ) on one of the rotor shafts ( 8, 9 ), forming the gear stage ( 37 ).

[0001] The present invention relates to a vacuum pump having thecharacterising features of patent claim 1.

[0002] Vacuum pumps of this kind belong to the class of two-shaft vacuumpumps. Typical examples of two-shaft vacuum pumps are Roots pumps, clawspumps and screw pumps. The two rotors of such pumps are located in apump chamber and effect pumping of the gases from an inlet to an outlet.The cantilevered bearing offers, in the instance of axially pumpingmachines, the benefit that on the suction side (high-vacuum side) shaftseals are not necessary.

[0003] In two-shaft machines with synchronised shafts, direct driving ofone of the two shafts is common (c.f. DE 198 20 523 A1, for example). Ifin machines of this type common AC drive motors are employed, thereresult rotor speeds of 3000 rpm. (at 50 Hz) and 3600 rpm. (at 60 Hz)respectively. Pumps being operated at such speeds have a low powerdensity, require narrow slots and/or many stages and are for this reasonrelatively large, heavy and costly. Increasing the speed would bepossible with the aid of a frequency converter; however, frequencyconverters for large drive power ratings are expensive.

[0004] A vacuum pump with the characterising features of patent claim 1is known from European patent 472 933, drawing FIG. 15. The drive motoris accommodated in a casing at the side next to the pump. In order to beable to operate the rotors at a higher speed compared to that of themotor, a gear is provided. The driving toothed gear of the motor shaftis coupled via a further toothed gear to a toothed gear arranged on oneof the rotor shafts. A solution of this kind requires much space.Moreover, four shafts are present which each need to be equipped withbearings.

[0005] It is the task of the present invention to design a vacuum pumpof the kind affected here in a more simple and more compact manner.

[0006] This task is solved through the characterising features of thepatent claims.

[0007] The essential advantage of the present invention is, that themeans which are required for a transmission to the higher speed—doublingof rotor speed, for example—are much simpler compared to thestate-of-the-art. Commonly employed motor technology can be retained. Inparticular when accommodating also the drive motor in the bearing/gearchamber, there result extremely slim and compact designs and in additioncooling of the electric motor is simplified.

[0008] Further advantages and details of the present invention shall beexplained with reference to examples of embodiments depictedschematically in drawing FIGS. 1 to 10. Depicted in

[0009] drawing FIGS. 1 to 3 are examples of embodiments according to thepresent invention, in which the motor rotor runs on a separate motorshaft arranged beside the rotor shafts and

[0010] drawing FIGS. 4 to 10 are examples of embodiments in which themotor rotor and one of the rotor shafts have a joint axis of rotation.

[0011] In the drawing figures, the two-shaft vacuum pump is designatedas 1, its rotors as 2, 3, its pump chamber as 4 and is pump chambercasing as 5. Adjoined to pump chamber casing 5 is the bearing/gearchamber 6, the casing of which is designated as 7. The rotor shafts 8, 9extend into the bearing/gear chamber 7. The axes of rotation of therotors and the shafts are designated as 11 and 12. The shafts aresupported by bearings on the side of the pump chamber and on the side oftheir ends (bearings 13 to 16) so that the rotors 2, 3 are supported ina cantilevered manner. The rotor shafts 2, 3 are coupled via asynchronising gear 17 being formed by two engaging toothed gears 18, 19.Gaskets 21, 22 are provided for the purpose of sealing off the pumpchamber 4 against the bearing chamber 6.

[0012] In all examples of the embodiments depicted, the drive motor 25is located in the bearing/gear chamber 7. The stator 26 encompasses thearmature 27 being affixed on to the motor shaft 28. The motor shaft 28extends in each instance in parallel to the rotor shafts 8, 9 and issupported by bearings in the area of its ends (bearings 31, 32) in thebearing/gear chamber 7. Its axis of rotation is designated as 29.

[0013] There also exists the possibility of arranging a standard motoroutside of casing 7 and to link said motor to a shaft extending withinthe bearing/gear chamber 6 in parallel to the rotor shafts 8, 9 with themotor shaft carrying the driving toothed gear 35. A solution of thiskind is outlined through the dashed line 30 in drawing FIG. 1.

[0014] As an example, a screw vacuum pump 1 is depicted in drawingFIG. 1. Plane 23 (drawing FIGS. 2, 3 and 4) formed by the axes ofrotation 11, 12, is perpendicular to the plane of the drawing figure, sothat only one rotating unit is visible. During their operation, therotors 2, 3 pump gases from inlet 33 to an outlet which is not depicted.

[0015] In the screw vacuum pump in accordance with drawing FIG. 1, themotor shaft 28 is adjoined at the side of the plane formed by axes ofrotation 11, 12. The motor shaft carries a driving toothed gear (drivinggear 35) which directly engages with a toothed gear (driven gear 36).Driving gear 35 and driven gear 36 form a gear stage 37. The driven gear36 is affixed on to one of the rotor shafts 8, 9. Synchronous driving ofthe second rotor shaft is in each instance effected through the toothedgears 18, 19 of the synchronising gear 17.

[0016] Drawing FIGS. 2 to 4 outline coupling options of the kinddetailed. In the solution according to drawing FIG. 2, the driving gear35 engages with one (18) of the two synchronising toothed gears 18, 19.The toothed gear 18 acts at the same time as the driven gear 36. Thetransmission ratio is determined by the ratio between the diameters ofthe toothed gears 35 and 18.

[0017] The embodiment in accordance with drawing FIG. 3 substantiallycorresponds to the solution depicted in drawing FIG. 1. Located underthe synchronising toothed gear 18 on the shaft 8, there is a further,toothed gear 36 preferably smaller in diameter, which engages with thedriving toothed gear 35. The same also applies to the solution inaccordance with drawing FIG. 4. The difference compared to drawing FIG.3 is that the axes of rotation 11, 12 and 29 are located in one plane.

[0018] From drawing FIGS. 2 to 4 it is apparent that on the one hand theusable space between the rotor shafts 8, 9 may be utilised in part forthe motor stator 26 (drawing FIGS. 2, 3) so that compact solutions willresult. On the other hand the angle between the respective axes ofrotation may be selected almost free of any restrictions.

[0019] In the embodiments in accordance with drawing FIGS. 5 to 10, themotor shaft 28 is designed to be hollow, so that there then exists thepossibility of letting one of the rotor shafts penetrate the hollowshaft 28 in such a manner that the axes of rotation 29 and 11respectively 12 are identical. In embodiments of this kind the usablespace between the rotor shafts 8, 9 may be utilised even better. In all,there results from this an optimally compact and slim shape.

[0020] Some of the design options for such embodiments are depicted indrawing FIGS. 5 to 10. In the solutions in accordance with the drawingFIGS. 5 and 6, the hollow shaft 28 carries in each instance the drivinggear 35 which engages with the driven gear 36 on the rotor shaft locatedbesides the hollow shaft 28. The synchronisation gears¹⁾ 17 offset whichrespect to this is employed for synchronised driving the rotor shaft 8penetrating the hollow shaft 28. Also in the drawing FIGS. 7 and 8 adriving gear 35 and a driven gear 36 form the gear stage 37. Outlined indrawing FIG. 7 is, that the gear stage is designed by way of chain orbelt²⁾ stages. The solution in accordance with drawing FIG. 8 isequipped with a planet gear.

[0021] The bearing arrangement for motor shaft 28 may be effectedindependently of the bearings 13 to 16 for rotor shafts 8, 9 by means ofcarriers affixed to the casing (drawing FIG. 8, upper bearing 31). Anespecially compact solution is attained when the motor shaft 28 issupported by at least one (drawing FIG. 8, bearing 32) preferably bothbearings 31, 32 (drawing FIGS. 5 and 7) on the rotor shaft 8 penetratingthe hollow shaft 28. Moreover, the rotor shaft 8 penetrating the hollowshaft 28 may be supported within the hollow shaft (bearings 15 indrawing FIG. 6). Finally there is depicted in drawing FIG. 7 as aspecial feature that the transmission ratio of the synchronising stagemay differ from 1:1. The toothed gears 18 and 19 have differingdiameters, outlining a transmission ratio of 2:1. Required for this isthat the rotors 2, 3 be designed correspondingly.

[0022] Drawing FIGS. 8 to 10 depict the way in which the hollow motorshaft 28 is coupled to the rotor shaft 8 centrally penetrating thehollow shaft, said coupling being effected by a planet gear 41, formingthe gear stage 37. The planet gear comprises in a manner which isbasically known the outer ring gear 42, for example two planet gears 43,44 as well as the sun gear 45 affixed to the rotor shaft 8 with axis ofrotation 29. Schematic diagram 9 depicts the solution presented indrawing FIG. 8 with a fixed ring gear 42. The plant gears 43, 44 whichare joined via cranks 46, 47 to the motor shaft 28, form the drivinggears 35, 35′. Only one planet gear 44 would suffice as the driving gear35 (drawing FIG. 9). The sun gear 45 forms the driven gear 36.

[0023] In the solution in accordance with drawing FIG. 10 the ring gear42 forms the driving gear 35. For the planet gear 44 ³⁾ a fixed carrieris provided. The sun gear 45 again forms the driven gear 36. Although inthe instance of this solution the driving gear 35 and the driven gear 36no not engage directly, the aims of the invention—compact, simple—can beattained.

[0024] It has already been proposed to equip at least one of the rotorshafts 8, 9 with a central bore and to utilise said bore(s) forconveying a lubricating and cooling agent (preferably oil). Where thedrive motor 25 is arranged within the bearing/gear chamber, said motormay also be cooled with the oil. An oil pump for pumping the oil may bearranged on one of the shafts 8, 9 or 28. If the motor shaft 28 shouldbe located besides the rotor shafts 8, 9 then a particularly expedientsolution is such that the oil pump—preferably designed as an eccentricpump—be arranged on the motor shaft 28, specifically in the area of itsupper end. This embodiment is depicted in drawing FIG. 1. The oil pumpis designated as 51. In addition, one of the shafts 8, 9 or 28 may berun out, on its side adjacent to the pump chamber, from the bearing/gearchamber 6 in a sealed manner and carry a ventilating wheel 52.Expediently, to this end also the motor shaft 28 is utilised inaccordance with drawing FIG. 1.

1. Vacuum pump (1) comprising a pump chamber casing (5) accommodatingtwo co-operating rotors (2, 3) which are respectively arranged on ashaft (8, 9); a bearing/gear chamber (6) adjacent to the pump chambercasing (5), in which the rotor shafts (8, 9) are cantilevered andprovided with a synchronisation gear (17); a drive motor (25) whosedrive shaft (28) extends parallel to the rotor shafts (8, 9) and isprovided with a drive gear (35); also comprising a gear stage (37)between the drive shaft (28) and one of the rotor shafts (8, 9), whereinthe drive gear (35) of the drive shaft (28) engages directly with adriven gear (36) on one of the rotor shafts (8, 9), forming the gearstage (37).
 2. Pump according to claim 1, wherein the drive gear (35) ofthe drive shaft (28) engages with one of the toothed gears (18, 19) ofthe synchronisation gear (17) having, compared to the driving gear (35),a smaller diameter.
 3. Pump according to claim 1, wherein the drive gear(35) of the drive shaft (28) engages with a toothed gear (36) on one ofthe rotor shafts (8, 9), said toothed gear having, compared to thesynchronising toothed gear (18 and 19 respectively) on this shaft, asmaller diameter.
 4. Pump according to one of the above claims, whereinthe drive motor (25) is accommodated within the bearing/gear chamber(6).
 5. Pump according to claim 4, wherein the motor shaft (28) islocated beside the rotor shafts (8, 9).
 6. Pump according to claim 5,wherein at one end of the motor shaft (28), preferably at it's end onthe pump chamber side, there is located an oil pump (51).
 7. Pumpaccording to claim 5 or 6, wherein the motor shaft (28) is run, at itsend adjacent to the pump chamber, out of the gear/bearing chamber (6)and carries a ventilating wheel (52).
 8. Pump according to claim 4,wherein the drive shaft (28) of the drive motor (25) is of hollow designand where one of the rotor shafts (8, 9) penetrates the hollow driveshaft (28).
 9. Pump according to claim 8, wherein the rotor shaft (8 and9 respectively) penetrating the hollow shaft (28) is supported by thecasing (7) via bearings (13, 15) and where at least one of the twobearings (31, 32) of the motor shaft (28) is supported on the rotorshaft (8 and 9 respectively).
 10. Pump according to claim 8, wherein therotor shaft (8 and 9 respectively) penetrating the hollow shaft (28) issupported by at least one bearing (31 and 32 respectively) in the hollowshaft (28).
 11. Pump according to one of the claims 8, 9 or 10, whereinas the gear stage (37) there is provided a planet gear (41) with a fixedring gear (42).
 12. Pump according to one of the claims 1 to 10, whereina chain or belt stage forms the gear stage (37).
 13. Vacuum pump (1)comprising a pump chamber casing (5) accommodating two co-operatingrotors (2, 3) which are respectively arranged on a shaft (8, 9); abearing/gear chamber (6) adjacent to the pump chamber casing (5),wherein the rotor shafts (8, 9) are cantilevered and provided with asynchronisation gear (17); a drive motor (25) whose drive shaft (28)extends parallel to the rotor shafts (8, 9) and is provided with a drivegear (35); also comprising a gear stage (37) between the drive shaft(28) and one of the rotor shafts (8, 9), wherein the drive shaft (28) ofthe drive motor (25) is of hollow design, where one of the rotor shafts(8, 9) penetrates the hollow drive shaft (28) and where as the gearstage (37) a planet gear (41) with driven ring gear (42) and a fixed sunwheel is provided.
 14. Pump according to one of the above claims,wherein the synchronising gear (17) has a transmission ratio differingfrom 1:1.
 15. Pump according to one of the above claims, wherein thetoothed gears employed in the pump are made of plastic for the purposeof reducing noise.